Environmental Surveillance of Vector-Borne Diseases in a Non-Sewered System: A Case Study in Mozambique

Arboviral diseases pose major economic and social threats in less economically developed countries (LEDCs), where monitoring is challenging, especially in rapidly growing cities with informal settlements. In this study, we aimed to explore environmental surveillance (ES) in a non-sewered setting as a complement to syndromic surveillance in Maputo, Mozambique. Water samples were collected from nine points along the Infulene River (n = 66) in Maputo, Mozambique from February to September 2023. The presence of arboviruses (Dengue (DENV), Chikungunya (CHIKV), West Nile (WNV), and Usutu (USUV) virus) was determined by RT-qPCR. For the specific detection of CHIKV, two RT-qPCR assays were used: the Nsp1, targeting the non-structural protein 1 gene (nsP1) and the E1, targeting the E1 envelope protein gene (E1). DENV was detected in 82% (54/66) of the samples, with a median viral RNA load of 2.7 × 10^-2 (2.2 × 10⁵ copies/L (cp/L)), while CHIKV was detectable in 98% (65/66) of the samples, with a median viral RNA load of 4.8 × 10^-2 (2.2 × 10⁵ cp/L) for the nsP1 gene and 8.0 × 10^-2 for the E1 gene (4.8 × 10⁵ cp/L), and USUV was detected in 6% (4/66) of the samples at a median viral RNA load of 4.1 × 10^-7 (0 cP/L), with viral RNA load in positive samples varying between 1.8 × 10^-3 (7.1 × 10² cp/L) and 4.95 × 10^-2 (2.1 × 10³ cp/L). WNV was not detected throughout the study. The prevalence and concentration varied across sampling dates. Our study demonstrated the potential of ES as a tool for assessing the circulation of arboviruses in Mozambique, where a sewered system is unavailable. Consequently, ES could be expanded from polio surveillance to include other targets in LEDCs.